docs: def load_file(folder_path, idx, corpus):
          """
          Load speaker, file, utterance, labels for the file with the given id.
          """
          xml_path = os.path.join(folder_path, '{}.xml'.format(idx))
          wav_paths = glob.glob(os.path.join(folder_path, '{}_*.wav'.format(idx)))
  
          if len(wav_paths) == 0:
              return []
  
          xml_file = open(xml_path, 'r', encoding='utf-8')
          soup = BeautifulSoup(xml_file, 'lxml')
  
          transcription = soup.recording.cleaned_sentence.string
          transcription_raw = soup.recording.sentence.string
          gender = soup.recording.gender.string
          is_native = soup.recording.muttersprachler.string
          age_class = soup.recording.ageclass.string
          speaker_idx = soup.recording.speaker_id.string
  
          if speaker_idx not in corpus.issuers.keys():
              start_age_class = int(age_class.split('-')[0])
  
              if start_age_class < 12:
                  age_group = issuers.AgeGroup.CHILD
              elif start_age_class < 18:
                  age_group = issuers.AgeGroup.YOUTH
              elif start_age_class < 65:
                  age_group = issuers.AgeGroup.ADULT
              else:
                  age_group = issuers.AgeGroup.SENIOR
  
              native_lang = None
  
              if is_native == 'Ja':
                  native_lang = 'deu'
  
              issuer = issuers.Speaker(speaker_idx,
                                       gender=issuers.Gender(gender),
                                       age_group=age_group,
                                       native_language=native_lang)
              corpus.import_issuers(issuer)
  
          utt_ids = []
  
          for wav_path in wav_paths:
              wav_name = os.path.split(wav_path)[1]
              wav_idx = os.path.splitext(wav_name)[0]
              corpus.new_file(wav_path, wav_idx)
              utt = corpus.new_utterance(wav_idx, wav_idx, speaker_idx)
              utt.set_label_list(annotations.LabelList.create_single(
                  transcription,
                  idx=audiomate.corpus.LL_WORD_TRANSCRIPT
              ))
              utt.set_label_list(annotations.LabelList.create_single(
                  transcription_raw,
                  idx=audiomate.corpus.LL_WORD_TRANSCRIPT_RAW
              ))
              utt_ids.append(wav_idx)
  
          return utt_ids